THE Australian Bureau of Meteorology prepares the Australian temperature record from readings of temperature from sites throughout Australia. These readings are the raw data.
Recently a group of researchers including scientist and author Dr Jennifer Marohasy have questioned the accuracy of the record, because the final temperatures from the record differ from the raw data.
Dr Marohasy found the raw data has been adjusted or ‘‘homogenised’’ by the bureau so that warming appears where no warming or less warming was shown by the raw data.
Sometimes there is a valid reason for adjusting raw temperature data. In his 1996 thesis Simon Torok analysed the temperature sites around Australia and found several sites that required adjustments. This was because there was a discontinuity in the data, either a gap where the data was stopped, or a fluctuation that was inconsistent with what could be expected from the climate.
Torok provided some typically Australian examples of discontinuities such as cockatoos destroying thermometers and a suspicion that unusually hot records at one site were because the site recorder increased the temperature so his council worker friends could have the day off with pay.
A common reason for an unusual temperature is a move in the position of the thermometer.
It is crucial adjustments have some valid reason to justify them and, most importantly, the adjustment does not increase or alter the trend in the raw data.
However, it seems adjustments at several sites have occurred without genuine evidence of a discontinuity in the raw data.
In the analysis of the temperature records compared with the raw data, Dr Marohasy found adjustments that create a warming temperature trend without any support for changing the data.
At Bourke, a long temperature record going back to 1880 has effectively been truncated to 2000. The researchers discovered the raw data showed an Australian maximum temperature record of 51.7degrees Celsius on January 3, 1909. This record is no longer used by the bureau. Overall, Bourke raw data shows a cooling maximum temperature trend from 1880 of 1.7degrees a century. After adjustment, the temperature record at Bourke shows a slight warming temperature trend. This change of maximum temperature trend has a great effect on the whole of Australia’s temperature record. The bureau has offered no reason for the adjustments.
In the Newcastle region, the temperature site at Williamtown also shows a marked difference between raw minimum temperature data and the temperature record after adjustment by the bureau.
Government policy is based on climate data, which needs to be reliable, and this includes temperature records.
If possible faults with the temperature record are found, there is an obligation to investigate.
Anthony Cox is a Newcastle lawyer with an interest in climate